Compact edge illuminated diffractive display

ABSTRACT

There is provided a projection display device comprising: a light source, an SBG device comprising a multiplicity of separately SBG elements sandwich between transparent substrate to which transparent electrodes have been applied. The substrates function as a light guide. A least one transparent electrode comprises plurality of independently switchable transparent electrodes elements, each electrode element substantially overlaying a unique SBG element. Each SBG element encodes image information to be projected on an image surface. Light coupled into the light guide, undergoes total internal reflection until diffracted out to the light guide by an activated SBG element. The SBG diffracts light out of the light guide to form an image region on an image surface when subjected to an applied voltage via said transparent electrodes.

REFERENCE TO PRIORITY APPLICATION

This application claims the priority of U.S. Provisional PatentApplication No. 61/272,601 with filing date 9 Oct. 2009 entitled“Compact edge illuminated diffractive display”.

REFERENCE TO EARLIER APPLICATIONS

This application incorporates by reference in their entireties PCTApplication No. PCT/US2004/014124 by Popovich et al, entitled“Switchable Viewfinder Display”; PCT Application No PCT/IB2008/001909 byPopovich et al, entitled “Laser Illumination Device”; PCT Application NoPCT US2006/043938 by Popovich et al, entitled “Method and Apparatus forSwitching a PDLC device” and U.S. Provisional Patent Application No.61/272,601 with filing date 9 Oct. 2009 entitled “Compact edgeilluminated diffractive display”.

BACKGROUND OF THE INVENTION

This invention relates to a display device, and more particularly to acompact edge-illuminated projection display based on switchable Bragggratings.

There is growing consumer demand for projection displays that can bebuilt into mobile devices such as mobile telephones and hand-heldcomputers. However, image sizes and resolutions required for typicalapplications such as internet browsing or viewing high definition filmsare already beyond the scope of display technologies currently availablefor use in mobile devices. New ultra compact projectors known aspicoprojectors provide one solution to this problem. Many of thepicoprojector designs considered to date rely on conventional flat paneldisplay technologies such as Liquid Crystal Display (LCD) or DigitalLight Processor (DLP) technology such as that developed by TexasInstruments (TX). Optical design limits the miniaturization possiblewith either approach, even when solid state lasers are used as the lightsource. An alternative approach is to scan the image usingmicro-optical-electrical-mechanical systems (MOEMS), essentially writingthe image using a flying spot. Although MOEMS are much smaller than LCDsor DLPs they present complex opto-mechanical design problems. Very highscanning speeds, resolutions and the tight synchronization of mirrordriver and laser modulation are needed in order to deliver highresolution images. Achieving the mechanical robustness required inportable applications is also a challenge. A further problem is that itis also difficult to correct laser speckle in scanned displays.

Desirably, display technologies for portable devices should be verycompact with volumes of a few cubic centimeters. A thin form-factor isdesirable for ease of integration into devices such as mobiletelephones.

There is a requirement for a compact solid-state high-resolution dataprojection display with a thin form factor.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide compact solid-statehigh-resolution data projection display with a thin form factor.

A projection display device according to the principles of the inventioncomprises: a first light source emitting light of a first wavelength; afirst SBG device comprising a multiplicity of separately switchable SBGelements disposed in a single layer; transparent substrates sandwichingthe SBG device, said substrates together functioning as a first lightguide; and a means for coupling the first wavelength light into thefirst light guide. The first wavelength light undergoes total internalreflection within the first light guide. Transparent electrodes areapplied to opposing faces of the substrates. At least one of thetransparent electrodes comprises a plurality of independently switchabletransparent electrode elements. Each electrode element overlays a uniqueSBG element. Each SBG element in first SBG device diffracts firstwavelength light to form an image region on an image surface whensubjected to an applied voltage via the transparent electrodes.

In one embodiment of the invention the image surface is disposed inproximity to the display.

In one embodiment of the invention the image surface is disposed morethan 25 centimeters from said display.

In one embodiment of the invention the image surface is disposed morethan 50 centimeters from said display.

In one embodiment of the invention one image region comprises an imageof a keyboard.

In one embodiment of the invention the image region is an image pixel.

In one embodiment of the invention an SBG element pre-distorts the shapeof the image region.

In one embodiment of the invention the image surface is an opticaldiffusing material.

In one embodiment of the invention the image surface is the retina of aneye.

In one embodiment of the invention the image surface is a curvedsurface.

In one embodiment of the invention the display further comprises: atleast one infrared source; means for directing infrared light from theinfrared source towards the image surface and at least one infraredsensor operative to detect light scatter from an object disposed inproximity to the image surface. The infrared source may be a laser. Theinfrared sensor may comprise an image sensing array and lens.

In one embodiment of the invention the display further comprises: atleast one infrared source; means for directing infrared light from theinfrared source towards the image surface and at least one infraredsensor operative to detect light scatter from an object disposed inproximity to the image surface. The first SBG device contains at leastone infrared diffracting SBG element operative to diffract infraredlight from the infrared source towards the image surface when theinfrared diffracting SBG element is subjected to an applied voltage viathe transparent electrodes.

In one embodiment of the invention that provides full-colour imaging thedisplay further comprises: second and third light sources emitting lightof second and third wavelengths; second and third SBG devices eachcomprising a multiplicity of separately switchable SBG elements disposedin a single layer, the SBG elements of the first second and third SBGdevices substantially overlapping each other; transparent substratessandwiching the second SBG device, said substrates together functioningas a second light guide; transparent substrates sandwiching the thirdSBG device, said substrates together functioning as a third light guide;and means for coupling the first, second and third wavelength light intothe first, second and third light guide. Transparent electrodes areapplied to substrate faces in contact with the second and third SBGdevices. At least one of the transparent electrodes in contact with thesecond and third SBG devices comprises a plurality of independentlyswitchable transparent electrodes elements, each of the independentlyswitchable electrodes substantially overlays a unique SBG element. Thefirst, second and third wavelength light undergoes total internalreflection within the light guides, Each element of the second SBGdevice diffracts second wavelength light to form a second image regionon an image surface when subjected to an applied voltage via thetransparent electrodes. Each element of the third SBG device diffractsthird wavelength light to form a third image region on an image surfacewhen subjected to an applied voltage via the transparent electrodes. Thefirst, second and third image regions substantially overlap.

In one embodiment of the invention that provides full colour imaging SBGelements in the first, second and third wavelength SBG devices areactivated in bands. Each band comprises at least one row of SBGelements. Each band is continuously scrolled vertically. At least oneband in each of the first, second and third SBG devices is activated atany instant with no overlap occurring between the first, second andthird wavelength SBG device bands.

A more complete understanding of the invention can be obtained byconsidering the following detailed description in conjunction with theaccompanying drawings wherein like index numerals indicate like parts.For purposes of clarity details relating to technical material that isknown in the technical fields related to the invention have not beendescribed in detail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevation view of one embodiment of theinvention.

FIG. 2 is a schematic front elevation view of a detail of an SBG devicein one embodiment of the invention.

FIG. 3 is a schematic side elevation view of one embodiment of theinvention.

FIG. 4 is a schematic side elevation view of one embodiment of theinvention.

FIG. 5 is a schematic plan view of the embodiment of the inventionillustrated in FIG. 4.

FIG. 6 is a schematic side elevation view of one embodiment of theinvention.

FIG. 7 is a schematic front elevation view of a scrolling SBG device inone embodiment of the invention.

FIG. 8 is a front elevation view of structured illumination provided byone embodiment of the invention.

FIG. 9 is a front elevation view of structured illumination provided byone embodiment of the invention.

FIG. 10 is a schematic side elevation view of one embodiment of theinvention incorporating an infrared source and infrared detector.

FIG. 11 is a schematic plan view of one embodiment of the inventionincorporating an infrared source and an infrared detector.

FIG. 12 is a schematic side elevation view of one embodiment of theinvention incorporating an infrared source and an infrared detector.

FIG. 13 is a schematic plan view of an embodiment of the invention thatprovides a virtual keyboard.

FIG. 14 is a schematic side elevation vies of an embodiment of theinvention that uses reflective SBGs.

DETAILED DESCRIPTION OF THE INVENTION

It will apparent to those skilled in the art that the present inventionmay be practiced with some or all of the present invention as disclosedin the following description. For the purposes of explaining theinvention well-known features of optical technology known to thoseskilled in the art of optical design and visual displays have beenomitted or simplified in order not to obscure the basic principles ofthe invention.

Unless otherwise stated the term “on-axis” in relation to a ray or abeam direction refers to propagation parallel to an axis normal to thesurfaces of the optical components used in the embodiments of theinvention. In the following description the terms light, ray, beam anddirection may be used interchangeably and in association with each otherto indicate the direction of propagation of light energy alongrectilinear trajectories.

Parts of the following description will be presented using terminologycommonly employed by those skilled in the art of optical design.

It should also be noted that in the following description of theinvention repeated usage of the phrase “in one embodiment” does notnecessarily refer to the same embodiment.

The compact projection display disclosed in the present application isbased on a diffractive optical device known as a Switchable BraggGrating (SBG). A SBG is a Bragg grating recorded into a polymerdispersed liquid crystal (PDLC) mixture. Typically, SBG devices arefabricated by first placing a thin film of a mixture ofphotopolymerizable monomers and liquid crystal material between parallelglass plates. One or both glass plates support electrodes, typicallytransparent indium tin oxide films, for applying an electric fieldacross the PDLC layer. A Bragg grating is then recorded by illuminatingthe liquid material with two mutually coherent laser beams, whichinterfere to form the desired grating structure. During the recordingprocess, the monomers polymerize and the PDLC mixture undergoes a phaseseparation, creating regions densely populated by liquid crystalmicro-droplets, interspersed with regions of clear polymer. Thealternating liquid crystal-rich and liquid crystal-depleted regions formthe fringe planes of the grating. The resulting Bragg grating canexhibit very high diffraction efficiency, which may be controlled by themagnitude of the electric field applied across the PDLC layer. In theabsence of an applied electric field the SBG remains in its diffractingstate. When an electric field is applied to the hologram via theelectrodes, the natural orientation of the LC droplets is changed thusreducing the refractive index modulation of the fringes and causing thehologram diffraction efficiency to drop to very low levels. Thediffraction efficiency of the device can be adjusted, by means of theapplied voltage, over a continuous range from essentially zero to near100%. U.S. Pat. No. 5,942,157 by Sutherland et al. and U.S. Pat. No.5,751,452 by Tanaka et al. describe monomer and liquid crystal materialcombinations suitable for fabricating ESBG devices.

In one embodiment of the invention illustrated in the schematic sideelevation view of FIG. 1 there is provided an SBG array devicecomprising a pair of transparent substrates 11 and 12 and an SBG layer20 sandwiched between the substrates. The two substrates 11 and 12together form a light guide. The SBG layer comprises an array ofindividually switchable SBG elements. As will be discussed below the SBGelements may be switched using a range of spatio-temporal switchingschemes, including any of the active matrix switching regimes used inconventional flat panel displays. Typically the substrates will befabricated from optical glass such as BK7 or a high quality opticalplastic.

Transparent electrodes, which are not shown in FIG. 1, are applied toboth of the inner surfaces of the substrates and electrically coupled toa voltage generator (not illustrated). The electrodes are configuredsuch that the applied electric field will be perpendicular to thesubstrates. Typically, the planar electrode configuration requires lowvoltages, in the range of 2 to 4 volts per μm. The electrodes wouldtypically be fabricated from Indium Tin Oxide (ITO). Commerciallyavailable ITO typically has a coating resistance of typically 300-500Ohm/sq. An exemplary ITO film used by the inventors is the N00X0325 filmmanufactured by Applied Films Corporation (Colorado). Typically, ITOfilms used with the present invention have a thickness of 100 Angstrom.

In one embodiment of the invention the electrode on one substratesurface is uniform and continuous, while the electrode on the opposingsubstrate surface is patterned to match the shapes of the SBG elements.In an alternative embodiment of the invention the electrodes may beidentically patterned such that each SBG element is sandwiched byidentical electrodes matching the shape of the SBG element. Desirably,the planar electrodes should be exactly aligned with the SBG elementsfor optimal switching of the symbols and the elimination of any imageartefacts that may result from unswitched grating regions.

In practice the SBG elements will separated by very narrow grating-freeregions which are essentially homogenous regions of PDLC that generallydo not respond to applied electric fields. Such grating-free regionsnormally result from masking during fabrication of the SBG device.Techniques for overcoming problems associated with such gaps aredisclosed in PCT Application No PCT US2006/043938 by Popovich et al,entitled “Method and Apparatus for Switching a PDLC device”, which isincorporated by reference herein in its entirety, may be used with thepresent invention. In most applications of the invention the effects onimage quality of such gaps between SBG elements are not likely to besignificant.

An SBG contains slanted fringes resulting from alternating liquidcrystal rich regions and polymer rich (i.e. liquid crystal depleted)regions. SBGs may be configured to be transmissive or reflectiveaccording to the slant of the fringes. Reflection SBGs are characterizedby fringes that are substantially parallel to the substrates. For thepurposes of explaining the invention transmissive SBGs will be assumedin the following description. However, it should be clear that any ofthe embodiments of the invention may be practiced using eitherreflective or transmissive SBGs. With no electric field applied, theextraordinary axis of the liquid crystals generally aligns normal to thefringes. The grating thus exhibits high refractive index modulation andhigh diffraction efficiency for P-polarized light. When an electricfield is applied to the SBG, the extraordinary axes of the liquidcrystal molecules align parallel to the applied field and henceperpendicular to the substrate. Note that the electric field due to theplanar electrodes is perpendicular to the substrate. In this state thegrating exhibits lower refractive index modulation and lower diffractionefficiency for both S- and P-polarized light. Thus the grating region nolonger diffracts light but rather acts like a transparent plate havelittle effect on incident light other than a small amount of absorption,scatter and Fresnel reflection loss at the grating-substrate interfaces.

The operation of a compact projection display according to theprinciples of the invention may be understood with reference to FIGS.1-3. FIG. 2 shows a front elevation view of the SBG array. FIG. 3 showsa side elevation view of the display. We consider the case in which oneSBG element 22 is in its active or diffracting state and all other SBGelements such as the one indicated by 21 are in their passive or nondiffracting states. Input light 1000 from a source 4 is opticallycoupled to the substrates 11 and 12 via an optical coupling device 3.Light admitted into the light guide undergoes TIR between the outersurfaces of the substrates 11,12. Advantageously, the source is a solidstate laser. Alternatively, the source may be a Light Emitting Diode(LED). However the broader spectral bandwidth of LEDs will result insome chromatic dispersion at the SBG elements. The coupling device maybe a prism or a grating. The invention does not assume any particularmethod for coupling light into the substrates. However, a method basedon a grating is highly desirable from the perspective of minimizing thethickness of the display. To overcome laser speckle the display wouldadvantageously also incorporate a despeckler such as the one disclosedin the PCT application PCT/IB2008/0019099 with International Filing date22 Jul. 2008 entitled “LASER ILLUMINATION DEVICES” which is incorporatedby reference herein in its entirety. The invention may be applied withany other type of despeckler but preferably one based on solid statetechnology.

The input light 1000 is deflected into the ray direction 1001 by thecoupling device 3. The deflection angle in the substrates should exceedthe critical angle for the substrate medium to air interface. The raynow follows a TIR path constrained by the outer surfaces of the lightguide provided by the substrates. Hence, the ray 1001 is totallyinternally reflected into the ray path indicated by 1001,1002,1003.

The grating in each SBG element encodes wave-front amplitude and phasemodulation information such that that incident TIR light is diffractedto form a focussed image region of predefined geometry and luminancedistribution at the image surface 5. The light 1003 which impinges onthe active SBG element 22 is diffracted towards the image surface 5 asthe beam 1004. As indicated in FIG. 3, the diffracted light 1004 formsan image 1100 at the image surface 5. Light which does not impinge onthe SBG element will hit the substrate-air interface at the criticalangle and is therefore totally internally reflected and eventuallycollected at a beam stop, which is not illustrated. The invention doesnot assume any particular method for trapping non diffracted light.

The image surface 5 may a diffusing surface of any geometry and asindicated in FIG. 3 may be tilted with respect to the display. Intypical applications of the invention the image surface will be a plane.The image surface will most typically will be either parallel to ororthogonal to the grating plane. The image is formed without the needfor an additional lens or any other optical element between the SBGarray and the surface. Another important feature of the invention isthat, since the SBG array elements each contain diffraction patterns,the resolution of the final projected images is much higher than theresolution of the array. The side elevation view of the display of FIG.1 in which the source and coupling optics are omitted shows theformation of an image element 1100 on the surface 5 by the SBG element22.

In one embodiment of the invention the image element may be arectangular pixel having a luminance level determined by the voltageapplied across the SBG element. By applying voltages to each SBG in theSBG array a pixelated image is provided over a predefined image area. AnSBG element may be designed to provide pre-distortion of the imageelement geometry to compensate for the effects of off axis projection,such as key-stoning. The invention is not necessarily limited topixelated display applications. In one embodiment of the invention theimage element formed by a SBG element may have an intensity distributionwithin a predefined area. As will be explained below such an embodimentmay be used to provide structured illumination for a range ofapplications.

The techniques for encoding such optical functions into an SBG are wellknow to those skilled in the design of Holographic Optical Elements(HOEs) and Diffractive Optical Elements (DOEs). The invention does notrely on any particular method of encoding optical functions into SBGs.Advantageously the SBG element is fabricated by first designing andfabricating a Computer Generated Hologram (CGH) with the requiredoptical properties and then recording the CGH into the ESBG element. Theabove process is equivalent to forming a hologram of the CGH. Theinvention does not rely on any particular method for recording the CGHinto the SBG. Any holographic recording techniques known to thoseskilled in the art of holography may be used. It should be noted thatthe resulting SBG element is not identical in every respect to the CGHsince properties of a CGH rely on its surface phase relief featureswhile the optical characteristics of a Bragg grating such as an SBG relyon a complex three dimensional fringe distribution.

It should be clear from consideration of FIGS. 1-3 that a displayaccording to the principles of the invention will be transparent toexternal ambient light such as the light 1005 indicated in FIG. 1. Sincethe external light is broadband and incident over a wide range of anglesonly a small portion of it will be lost due to diffraction at active SBGelements. In other words only a very small portion of the external lightwill have incidence angles and wavelengths that satisfy the Braggcondition at the active SBG elements. The external light will alsosuffer small transmission loss due to Fresnel reflections, scatter andabsorption.

Typically, the image surface is disposed between 25-100 centimeters fromthe display. However, the distances may be much greater depending onethe application and the image brightness requirements. In certainembodiments of the invention the image surface may be very close to thedisplay. In such embodiments the image and image surface may beintegrated within a directly viewable display module. However, suchembodiments will sacrifice the image magnifications obtained byprojecting the image over a longer distance.

In one embodiment of the invention based on the embodiment illustratedin FIGS. 1-3 there is provided a colour projection display. The basicprinciples of the colour display are illustrated in FIGS. 4-5. Lightfrom separate red green and blue sources is coupled into the light-guideformed by the substrates 11,12. Again the coupling optics, which are notillustrated, may comprise prisms or diffractive elements. Manyalternative methods of coupling light from different colour sources intoa light guide will be known to those skilled in the art. Desirably, thecoupling optics are based on diffractive optical techniques to keep thedisplay as thin as possible. The TIR angle for each colour isconstrained such that the incidence angle for a particular colour lightat a given SBG satisfy the Bragg condition for diffraction at aspecified diffraction angle. The red, green, blue light is presentedsequentially. As indicated in the schematic side elevation view of FIG.4, incident red, green, blue TIR rays 1003R,1003G,1003B at the SBG 22are diffracted into the red, green, blue image light indicated by1004R,1004G,1004B towards the image surface 5 forming the colour imageelement 1100. FIG. 5 shows a plan view of the display showing the a planview of the diffracted beams indicated by 1005R,1005G,1005B. The lateralextent of the projected beam is indicated by the rays 1006A, 1006B. Notethat in FIGS. 4-5 the separation of the beams has been exaggerated forthe purposes of explanation.

Colour imaging may also be provided by stacking red, green, and blue SBGarrays of the type illustrated in FIGS. 1-3 and providing illuminationfrom red, green and blue light sources. Such embodiments of theinvention will suffer from the problems of alignment and lighttransmission loss. In the embodiment of the invention illustrated in theschematic side elevation view of FIG. 6 there are provided red, greenand blue diffracting SBG arrays 20,30,40. The SBG arrays are sandwichedbetween substrates 11,12,13,14,15,16. The substrates are stacked to forma single light guiding structure. Light from separate red, green andblue sources is coupled into the light-guide. Again the preferredcoupling optics are based on diffractive optical techniques to keep thedisplay as thin as possible. Since a separate SBG arrays is provided foreach colour, the TIR angle may be the same for each colour. The red,green, blue light is presented simultaneously. Referring to FIG. 6incident red, green and blue light 1006R,1006G,1006B at the active red,green, blue SBG elements 22,32,42 is diffracted into the beams1007R,1007G,1007B forming a colour image element 1102 at the imagesurface 5. Note that the separation of the beams has again beenexaggerated for the purposes of explanation.

In one embodiment of the invention the SBG elements may be switchedusing a switching scheme commonly referred to as “scrolling”.Conventional colour displays rely on providing a single display panelthat is updated with red, green and blue picture information in turn andsequentially fully illuminated by red, green and blue illumination.Alternatively, three panel architectures provide seperate red, green andblue image panels which are separately fully illuminated by red, greenand blue light. Such displays suffer from the problems of having toupdate the entire red, green or blue images before illumination of theappropriate colour can be applied. In the case of three-panel displaysthe cost of the display may become prohibitive. A single panel scrollingcolor projection display system is characterized by a single lightmodulator panel having a raster of individual picture elements orpixels, which panel is illuminated by horizontally elongated red, greenand blue illumination bars or stripes. The stripes are continuouslyscrolled vertically across the panel while the rows of pixels aresynchronously addressed with display information corresponding to thecolor of the then incident stripe. The modulated scrolling red, greenand blue stripes are then projected onto a display screen to produce avisually integrated full color display. Exemplary scrolling displays aredisclosed in U.S. Pat. No. 5,410,370, entitled “Single panel colorprojection video display improved scanning” issued to P. Janssen on Mar.25, 1994, and U.S. Pat. No. 5,416,514, entitled “Single panel colorprojection video display having control circuitry for synchronizing thecolor illumination system with reading/writing of the light valve”issued to P. Janssen et al. on May 16, 1995.

The principles of scrolling may be applied in the present invention byswitching rows of SBG elements in sequence. A basic scrolling scheme foruse with the present invention is illustrated in FIG. 7. The scrollingscheme may be implemented using the embodiment of FIG. 6. In each SBGdevice SBG elements are activated in bands comprising at least one rowof SBG elements. The bands are continuously scrolled vertically, atleast one band in each of the red green and blue SBG devices beingactivated at any instant, said bands in said first, second and third SBGdevices not overlapping. FIG. 7 shows red, green and blue statesindicated by symbols R,G,B at one instant in time. In each case, thediffracting rows or bands of SBG elements are shaded. Thus red SBG band50R, green SBG band 50G and blue SBG band 50B are diffracting while redSBG pixel rows 51R, green SBG pixel rows 51G and blue SBG pixel rows 51Bare not diffracting permitting TIR to proceed.

In a particular group of embodiments of the invention at least one SBGarray element in any of the above described embodiments may providestructured infrared illumination using light from an infra red source.The infrared light would be injected into the light guide formed by thesubstrates in a similar fashion to the means used to introduce visiblelight in any of the above embodiments. The infrared source is typicallya 780 nm laser. However other near-infrared sources may be used. Thestructure lighting may comprise parallel bars, concentric circles andother geometrical structures commonly used in the visualization andmeasurement of three-dimensional shapes. Examples of structures infraredlighting are provided in FIGS. 8-9. In the example shown in FIG. 8 thestructured lighting 1010 comprises parallel bars and spaces 1011,1012.In the example shown in FIG. 9 the structure lighting 1020 comprisesconcentric circles 1021 separated by gaps 1022.

FIGS. 10-11 show an embodiment similar to the one of FIGS. 4-5 in whichthere is further provided at least one infrared sensor such as 7 and atleast one infrared source such as 8. Advantageously, the sensor is a twodimensional infrared array. The infrared source illuminates the imagesurface 5 with the infrared beam indicated by 1100. The infrared sensordetects backscattered light from objects within a field of viewindicated by 1200. The sensor is coupled to a processor which is in turncoupled to an image processor which is not illustrated. The opticalsystem is illustrated in plan view in FIG. 11. Since the display istransparent one or both of the infrared sensor or source may bedisplayed on the opposite site of the display to the image surface asindicated in FIGS. 10-11. Alternatively, one or both of the infraredsensor or source may be disposed around the periphery of the display. Inone embodiment of the invention a structured light pattern based on theones illustrated in FIGS. 8-9 may be encoded within the SBG element.Alternatively, other structured lighting patterns may be used.

In one embodiment of the invention illustrated in the schematic sideelevation view of FIG. 12 the infrared source may be coupled via thelight guide to one or more dedicated SBG arrays elements contained inthe SBG array. Totally internally reflected infrared light infraredlight 1009 incident on an active infrared diffracted diffracting SBGelement 23 is diffracted to provide the divergent infrared light beam1101. In one embodiment of the invention a structured light patternbased one the ones illustrated in FIGS. 8-9 may be encoded within theSBG element. Alternatively, other structured lighting patterns may beused. In one embodiment of the invention more than one infrareddiffracting SBG similar to the element 23 may be provided for thepurpose of determining object range by triangulation. Such animplementation of the invention may be used to provide the instantaneouslocation of an object near the image surface. The invention does notrely on particular method for determining range from triangulation ordetermined the shape of an object using structured light. Trackingalgorithms which are designed to determine the range or shape of anobject by analyzing changes in sequential image frames recorded by asingle sensor may also be used with the invention.

It will be clear from consideration of the above description that theinvention may be used to provide more than one viewable image. In oneembodiment of the invention based on the embodiments of FIGS. 10-12there is provided a virtual computer keyboard projected by a single SBGelement. The other SBG elements are used to project a live image, inother words an image that is updated on a frame-by-frame basis. One keywith symbol A is indicated by 1102. The infrared sensor 7 detectsinfrared light 1300 scattered from a finger 81 of the hand 8. An imageprocessing system (not illustrated) determines whether the proximity ofthe finger to the key is sufficiently close for a key strike to haveoccurred. In other embodiments of the invention more than one SBGelement may be used to project elements of the keyboard onto the imagesurface

The SGB arrays in any of the above described embodiments of theinvention may use SBG elements configured as wither transmissive orreflective gratings. In the embodiment illustrated in the schematic sideelevation view of FIG. 14 the SBG device 60 is based on reflectiongratings. TIR light indicated by 1040 is reflected by the active SBGelement 24 of the SBG device into the beam 1041 towards the imagesurface 51 forming the image 1103.

The SGB arrays in any of the above described embodiments of theinvention may incorporate SBG elements designed to diffract thermalinfra red radiation.

The SGB arrays in any of the above described embodiments of theinvention may incorporate SBG elements designed to diffract ultravioletradiation.

In one embodiment of the invention the image surface is the retina ofthe human eye.

Although the invention has been described in relation to what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed arrangements but rather is intended to cover variousmodifications and equivalent constructions included within the spiritand scope of the invention.

What is claimed is:
 1. A projection display for projecting image lightonto an image surface, said display comprising: a first light sourceemitting light of a first wavelength; a first SBG array comprising amultiplicity of separately switchable SBG elements disposed in a singlelayer; transparent substrates sandwiching said SBG array, saidsubstrates together functioning as a first light guide; transparentelectrodes applied to opposing faces of said substrates, at least one ofsaid transparent electrodes comprising a plurality of independentlyswitchable transparent electrode elements, each of said independentlyswitchable electrode elements substantially overlaying a unique SBGelement; a means for coupling said first wavelength light into saidfirst light guide, said first wavelength light undergoing total internalreflection within said first light guide; each said SBG element having adiffracting state and a non diffracting state; characterized in thateach said SBG element when in its diffracting state diffracts said firstwavelength light to form a focused image region of predefined geometryand luminance distribution on said image surface, wherein said SBGelement encodes wavefront and phase information corresponding to saidgeometry and said luminance distribution.
 2. The projection display ofclaim 1 wherein said diffracting state exists when no electric field isa applied across said SBG element via said transparent electrodes andsaid non diffracting state exists when an electric field is appliedacross said SBG element via said transparent electrodes.
 3. Theprojection display of claim 1 wherein the image surface is disposed inproximity to said display.
 4. The projection display of claim 1 whereinthe image surface is more than 50 centimeters from said display.
 5. Theprojection display of claim 1 wherein one said image region comprises animage of a keyboard.
 6. The projection display of claim 1 wherein saidimage region is an image pixel.
 7. The projection display of claim 1wherein said SBG elements pre-distort the shape of said image region. 8.The projection display of claim 1 wherein image surface is a diffusingmaterial.
 9. The projection display of claim 1 wherein image surface isthe retina of an eye.
 10. The projection display of claim 1 wherein saidimage surface is curved.
 11. The projection display of claim 1 furthercomprising: at least one infrared source; means for directing infraredlight from said source towards said image surface and at least oneinfrared sensor operative to detect light scattered from an objectdisposed in proximity to said image surface.
 12. The projection displayof claim 11 wherein said infrared source is a laser.
 13. The projectiondisplay of claim 11 wherein said infrared sensor comprises an imagesensing array and lens.
 14. The projection display of claim 11 whereinsaid first SBG array contains at least one infrared diffracting SBGelement operative to diffract infrared light from said infrared sourcetowards said image surface when said infrared diffracting SBG element issubjected to an applied voltage via said transparent electrodes.
 15. Theprojection display of claim 1 further comprising: second and third lightsources emitting light of second and third wavelengths; second and thirdSBG arrays each comprising a multiplicity of separately switchable SBGelements disposed in a single layer; said SBG elements of said first,second and third SBG arrays substantially overlapping; transparentsubstrates sandwiching said second SBG array, said substrates togetherfunctioning as a second light guide; transparent substrates sandwichingsaid third SBG array, said substrates together functioning as a thirdlight guide; transparent electrodes applied to substrate faces incontact with said second and third SBG arrays, at least one of saidtransparent electrodes in contact with said second and third SBG arrayscomprising a plurality of independently switchable transparentelectrodes elements, each of said independently switchable electrodessubstantially overlaying a unique SBG element; means for coupling saidfirst, second and third wavelength light into said first, second andthird light guides, said first, second and third wavelength lightundergoing total internal reflection within said light guides, eachelement of said second SBG array diffracting said second wavelengthlight to form a second image region on an image surface when subjectedto an applied voltage via said transparent electrodes, each said elementof said second SBG array when in its diffracting state diffracting saidsecond wavelength light to form a focused image region of predefinedgeometry and luminance distribution on said image surface, wherein saidelement of said second SBG array encodes wavefront and phase informationcorresponding to said geometry and said luminance distribution, eachelement of said third SBG array diffracting said third wavelength lightto form a third image region on an image surface when subjected to anapplied voltage via said transparent electrodes, each said element ofsaid third SBG array when in its diffracting state diffracting saidthird wavelength light to form a focused image region of predefinedgeometry and luminance distribution on said image surface, wherein saidelement of said third SBG array encodes wavefront and phase informationcorresponding to said geometry and said luminance distribution.
 16. Theprojection display of claim 15 wherein said first, second and thirdimage regions substantially overlap.
 17. The projection display of claim15 wherein in each said first, second and third wavelength SBG arraysaid SBG elements are configured in rows and columns of a rectangulararray and are switched sequentially into their diffracting states inbands comprising at least one row of SBG elements, wherein at least oneband of SBG elements in each of said first, second and third SBG arraysis activated at any instant, wherein no overlap exists between saidfirst, second and third wavelength SBG array bands.
 18. The projectiondisplay of claim 1 wherein the image surface is more than 25 centimetersfrom said display.